lets say i have 5^x and it equals 25 (5^2 = 25). we right that as
log5 25, correct?
to calculate that, use the log of the big number / log of small number. you put it into your calculator like this:
log(25) / log(5)
if your calculator works properly, it will tell you the answer is 2 :D

just remember ----> big number over little number (big as in how big you write it, not the value)